Saltcedar is an exotic shrub or small tree that has spread throughout the rivers, streams and lakes of west and southwest Texas and other areas of the western United States. This brochure explains an effort to introduce the saltcedar leaf beetle as a biological control measure against saltcedar. 8 pp., 3 photo

DeLoach, C.  Jack

Knutson, Allen E.

Muegge, Mark A.

Texas A&M University

A sustainable approach
using insect natural enemies
to suppress saltcedar infestations
 
L-5444
10/03
altcedar is an exotic shrub or
small tree that has spread throughout
the rivers, streams and lakes of west
and southwest Texas and other areas
of the western United States. In these
regions, saltcedar causes serious prob-
lems, including:
✶ Depleting groundwater
✶ Reducing stream flow
✶ Drying up lakes and reservoirs
✶ Increasing the salinity of the soil
surface
✶ Competing with forage grasses and
native plants
✶ Degrading wildlife habitat
Although saltcedar can be controlled
by herbicides and mechanical means,
these methods are expensive when used
over a large area. If applied improperly,
these techniques can also kill desirable
native plants.
Another control tactic is to use living
organisms to suppress saltcedar. This
method is called biological control.
To help control saltcedar, insects that
feed only on the plant are being intro-
duced into Texas and the western
United States.
S
Invader of rivers, lakes and wetlands
Saltcedar, also called tamarisk, is the com-
mon name for several species in the genus
Tamarix. These trees were introduced into the
United States from central Asia in the 1830s
and planted here as ornamentals and wind-
breaks and to stabilize river banks.
Three of those saltcedar species have
invaded rivers, lakes and other such rip-
arian habitats in 17 western states. In Texas,
large expanses of saltcedar grow along all
of the western river systems, including the
Canadian, Brazos, Colorado, Pecos and Rio
Grande.
Saltcedar has several characteristics that
help it grow across extensive areas and crowd
out native plants such as willows and cotton-
woods. The tree tolerates drought, heat, cold,
salinity, fire and flooding. Its roots extend
deeper into the soil than those of willow or
many other native riparian plants, and thus it
can spread further from streambanks and
extend across more of a flood plain. The
leaves of saltcedar concentrate and secrete
salt, which increases soil salinity beneath
saltcedar trees. 
Saltcedar has no economic value in the
United States and very little value to wildlife. 
(The athel tree, Tamarix aphylla, is planted
as a landscape ornamental in the southwest-
ern United States and Mexico. This species of
tamarisk is noninvasive and un-common in
natural areas. It is not a target of biological
control.)
Natural enemies
In its native range in Central Asia and the
Mediterranean, more than 350 species of
insects feed on saltcedar. But when saltcedar
was introduced into the United States, almost
all of these natural enemies were left behind.
Three of its natural enemies — one species
of leafhopper and two species of scale insects
— were accidentally introduced with the
saltcedar plants. Although these insects feed
specifically on saltcedar, they cause little
damage. As a result, saltcedar grows and re-
produces in the United States without the
many insect enemies that suppress its growth
in its native habitat.
Researchers are identifying the natural
enemies of the plant so that the insects can be
imported and established in the United States.
The USDA-Agricultural Research Service has
conducted research to identify insects that:
✶ Can be imported safely into the United
States
✶ Feed only on saltcedar
✶ Can kill saltcedar and reduce its spread
Saltcedar leaf beetle eggs and larva.
This and all U.S. biological control pro-
grams are regulated under the National
Environmental Policy Act and the USDA-
Animal and Plant Health Inspection Service
(APHIS). Exotic insects can be released only if
they have been approved by APHIS and the
participating state.
Insects proposed for introduction into the
United States are studied rigorously overseas
and in quarantine facilities in the United
States to ensure that they feed only on the tar-
get weed and that they do not threaten native
plants, nontarget species or economically
important plants.
Saltcedar is a good target for biological con-
trol as it has no close relatives in the United
States. Thus, there is very little risk that
insects that feed specifically on saltcedar will
attack any other plant. 
Saltcedar leaf beetle
The first insect approved for release in the
United States for biological control of saltcedar
is the saltcedar leaf beetle, Diorhabda elongata.
This insect was introduced from northern
China, Uzbekistan, Crete and Tunisia. 
Saltcedar beetles are yellow to yellow-
brown, about 1/4 inch (6 mm) long and shaped
like a cucumber beetle. Eggs are deposited in
masses of up to 20 eggs each, which are glued
to saltcedar foliage. The eggs hatch in about 5
days.
When small, the larvae are black. Larger
larvae are black with a yellow strip along
each side. Full-grown larvae are about 1/3 inch
(9 mm) long.
The larvae feed on saltcedar foliage for
about 3 weeks and then crawl or drop to the
ground, where they pupate in the leaf litter
on the soil surface. About a week later, adult
beetles emerge from the pupae. Two or more
generations are completed each year. Over
the winter, adults live beneath the leaf litter
and grasses on the soil surface.
For future release, researchers are studying
other insect species, including a small weevil,
a mealybug and gall insects.
Gradual death by defoliation
Saltcedar beetle larvae and adults feed on
the small, scalelike leaves of saltcedar. Larger
larvae and adults may also feed on the bark of
small twigs, causing the ends of the twigs to
dry up and die.
When a saltcedar leaf beetle feeds on
saltcedar leaves, they turn brown and die.
Large numbers of larvae can quickly defoliate
saltcedar trees. Although the trees can grow
new leaves, they are not expected to be able
to withstand repeated feeding by several gen-
erations of beetle larvae. 
Biological control of saltcedar will likely be
a gradual process. Before the trees begin to
die, they will need to be defoliated by
saltcedar beetles for one or more seasons.
Also, the beetles need time to reproduce so
that populations can grow large enough to
cause widespread damage to the trees. The
rate at which beetles fly to new sites is not
known.
Although biological control will not eradi-
cate saltcedar, it is expected to check the
tree’s growth and spread, allowing native
plants to be more competitive. 
Biological control is a sustainable approach
that can suppress saltcedar in the long term.
Control may be slow initially, but once bee-
tles are established in an area, they should
continue to reduce the regrowth of estab-
lished trees as well as the growth of seedling
saltcedar plants. 
Target dates for implementation
The saltcedar leaf beetle has been reared in
cages and studied at three research sites in
Texas for several years. In July 2003, research-
ers were granted federal and state approval to
release the beetle at six more sites in Texas.
Once populations of beetles are established
— expected in 2005 — beetles will be collect-
ed from these sites and distributed to
landowners, ranchers and public and private
agencies. The initial programs for distribution
will be limited by the availability of beetles. 
Much of the saltcedar infesting the Pecos
River has been treated recently with aerially
applied herbicides. Plans are to expand this
program to the Colorado River and other
areas. Biological control can complement
these herbicide programs, as the beetles can
help suppress the regrowth of surviving trees.
Biological methods are especially useful in
areas where herbicides cannot be applied
because of the potential harm to desirable
native vegetation, in environmentally sensi-
tive areas and in areas where there are too
few saltcedar trees to justify the cost of aerial
sprays.
Cooperating agencies  
The Saltcedar Biological Control Program
in Texas is a cooperative effort among many
federal, state, public and private agencies and
groups. The USDA-Agricultural Research
Service is the lead agency responsible for
identifying and testing insects approved for
biological control of saltcedar.
Other participating agencies include Texas
A&M University, Texas Cooperative Exten-
sion, Texas Agricultural Experiment Station,
Texas Department of Agriculture, USDA-
APHIS and the Colorado River Municipal
Water District. 
The national effort to biologically control
saltcedar is coordinated by the Saltcedar
Biological Control Consortium, an organiza-
tion of federal, state and private interests
devoted to improving natural and agricultural
ecosystems through the control of invading
saltcedar. 
For more information
For current information on the Saltcedar
Biological Control Program, contact the authors
or log onto:
http://bc4weeds.tamu.edu/saltcedar.html.
Authors
Allen Knutson, Mark Muegge  
and C. Jack DeLoach
Professor and Extension Specialist,
Assistant Professor and Extension Specialist,
The Texas A&M University System;
Research Entomologist,
Agricultural Research Service


English

Biological Control of Saltcedar

https://oaktrust.library.tamu.edu/bitstream/1969.1/87204/1/pdf_1854.pdf

Biological Control of Saltcedar

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